Mechanism analysis of steel frames considering moment–shear interaction

Considering the interaction of flexural moment and shear force in the steel frames with haunch or intermediate beam length and eccentrically braced frames with intermediate link length is a major concern of the structural analysis and design. This article contains two stages. In the first stage, to investigate the moment–shear interaction for the highly ductile steel I-sections, a study is carried out using finite element analysis and a simple and practical relationship is developed. In the second stage, a simple approach based on virtual work method for assemblage of interconnected rigid bodies is employed to consider collapse mechanisms with mixed hinges. Using this approach, the applicability of the proposed relationship is demonstrated for a one-bay portal frame by considering all possible collapse mechanisms including those containing mixed hinges. Some numerical examples are presented using the proposed approach. Results indicate that, in general, the effect of moment–shear interaction on the load capacity of the structures cannot be ignored, and the capacity could be estimated, without using step-by-step analysis. Finally, by satisfying kinematic compatibility requirements and normality condition, simplified relations are derived to estimate post-mechanism deformations of plastic hinges for a prescribed lateral drift